(Not Applicable)
(Not Applicable)
This invention relates to antennas and, more particularly, whip antennas operable over more than one frequency band.
The design and implementation of many varieties of whip antennas are well known. The dictionary definition of xe2x80x9ca flexible radio antennaxe2x80x9d encompasses the typical configuration of a base-supported upright element of extended length. Prior types of whip antennas are suitable for many applications, subject to inherent limitations such as usable frequency band for an individual antenna design and inadequacies where operation over a number of bands is required.
Objects of the present invention are, therefore, to provide new and improved whip antennas and such antennas having one or more of the following characteristics and advantages:
multi-band operation;
operation over a plurality of sub-bands (e.g., coverage from 30 to 90 MHz);
switch control of effective antenna length;
switchable length by electronic control;
dipole gain performance;
low reflection loss;
gain increase by increased antenna height for higher frequency bands;
simplified, low cost construction; and
base mount construction.
In accordance with the invention: a whip antenna, with switchable operative length for multi-band operation, includes an upper antenna element having a vertical axis and a choke section coaxial to the vertical axis below the upper antenna element. At least one coaxial line section is positioned along the vertical axis below and spaced from the choke section. The antenna may include at least one transmission line section in a non-coaxial position relative to the vertical axis and in spaced relation below the coaxial line sections. A plurality of switch devices is arranged to selectively couple the coaxial line and transmission line sections in series with the choke section. A driver configuration is coupled to the switch devices to selectively activate the switch devices to enable operation in a plurality of frequency bands. The antenna also includes a coaxial cable extending vertically along the vertical axis through the choke section and each coaxial line section and having a center conductor connected to the upper antenna element and an outer conductor connected to the choke section.
In one embodiment of the invention, the driver configuration is arranged to selectively activate the switch devices to provide any one of the following: the combination of the upper antenna element and the choke section, comprising a dipole operable in an upper frequency band; the combination of the upper antenna element, the choke section and at least one coaxial line section, these sections coupled in series via activation of at least one switch device to comprise a dipole operable in an additional frequency band lower than such upper frequency band; and the combination of the upper antenna element, the choke section, at least one coaxial line section and at least one transmission line section, these sections coupled in series via activation of a plurality of switch devices to comprise a dipole operable in a frequency band lower than the additional frequency band.
Also in accordance with the invention, a whip antenna, with switchable operative length for multi-band operation, and having an upper antenna element and choke section as described above may include first, second, third and fourth coaxial line sections respectively positioned below the choke section at successively lower positions. A plurality of switch devices is arranged to selectively couple to the choke section any one of (a) the first coaxial line section, (b) the first and second coaxial line sections, (c) the first, second and third coaxial line sections, and (d) the first second, third and fourth coaxial lines sections. In a particular configuration to provide operational coverage from 30-90 MHz, components of the antenna may have nominal vertical dimensions as follows:
upper antenna element, 1.30 meters;
choke section, 0.60 meters;
first coaxial line section, 0.52 meters;
second coaxial line section, 0.36 meters;
third coaxial line section, 0.13 meters; and
fourth coaxial line section, 0.08 meters.